The use of electrical stimulation of a carcass to expedite tenderizing is well known as evidenced by U.S. Pat. No. 2,544,681 to Harsham et al. It is recognized in that patent electrical stimulation results in an accelerated postmortem drop in the pH of the animal tissue and that this accelerated pH drop is beneficial to beef tenderness. Subsequent work in the field has shown that electrical stimulation of muscle rapidly depletes adenosine triphosphate (ATP) from the muscle. This chemical is necessary for muscle contraction to take place. Chilling of muscle (which is a common procedure in the meat packing industry) while the ATP level is still high results in a contraction or shortening of the muscle which produces an undesirable toughness. Depletion of ATP before chilling by means of electrical stimulation prevents or considerably reduces contraction and provides for much more tender beef.
It is generally accepted that the earlier the voltage stimulation is applied to the carcass after slaughter, the more effective is the stimulation in producing tenderness. However, there is wide disagreement in other respects, such as the level of the applied voltage, the manner in which it is applied, the body parts to which it is applied, the repetition rate of applied pulses, etc. Broadly speaking, there are three alternative techniques which have received some degree of acceptance in the meat packing industry. In a first of these techniques the carcass, after being suspended from the bleeding rack and bled, is transported along a path wherein the carcass makes rubbing contact with an electrified rail, the contact being generally at the shoulder region. The return path for current is through support hooks deployed in the Achilles tendon of one or both hind legs. Peak voltages on the order of one thousand volts are used and, in fact, are necessary to overcome the high contact resistance provided by the moving rubbing contact of the carcass along the rail. Such high voltages require carefully designed safety procedures and equipment which add to the expense and complexity of the system. Further, the suspended carcass may jerk spasmodically away from the contact rail, breaking contact and causing additional danger to personnel. Other disadvantages of this system include damage to the hide or marking of the carcass due to resistive heating at the contact rail.
A second system uses two roller hooks connected to the two hind legs so that current flows down one leg and up the other. High voltages are also necessary in this system in order to overcome the resistance of the two hind legs and Achilles tendons. The resulting need for personnel safety procedures and equipment renders this system expensive. In addition, there is some question as to whether this system is efficient in tenderizing all usable parts of the carcass.
Both of the systems described above require a length of rail in the middle of the dressing line which is long enough to permit entry and exit plus stimulation for a duration on the order of ninety seconds. In order to adopt such a system, considerable alterations are required in the packing plant.
A third system, which requires minimal alteration in an existing plant, employs a rectal probe which is manually inserted. The applied electrical stimulation takes the form of a series of low voltage pulses having a repetition rate of forty pulses per second and is applied for ninety seconds. This method avoids the safety problems inherent in the use of high voltage and is particularly effective, although the reason for the effectiveness has not heretofore been fully understood. It has a disadvantage in that the probe must be inserted before the animal is hoisted and bled rather than at a more desirable location along the line. In addition, the probe employed includes a pair of electrodes in the form of bent wires which are orthogonally positioned in crossing planes. Insertion, cleaning, and, most importantly, effectiveness as an electrode are poor at best.